The reconstruction of a 3-D model for the knee's articulating bones is a key component of computer-aided knee surgery systems. The existence of a pre-operatively acquired model enables the surgeon to pre-plan a surgery by choosing the proper implant size, calculating the femoral and tibial cutting planes, and evaluating the fit of the chosen implant. The conventional method of generating the 3-D model is segmentation of computed tomography (“CT”), or magnetic resonance imaging (“MRI”) scans, which are the conventional imaging modalities for creating patient-specific 3-D bone models. The segmentation methods used are either manually, semi-automatic, or fully automated. Although these methods are produce highly accurate models, CT and MRI have inherent draw backs, i.e., both are fairly expensive procedures (especially for the MRI), and CT exposes the patient to ionizing radiation. These limitations have motivated the research of new methods for acquiring and reconstructing bone models.
One alternative method of forming patient-specific models is the use of previously acquired X-Ray images as a priori information to guide the morphing of a template bone model whose projection matches the X-Ray images. Several X-Ray based model reconstruction methodologies have been developed for the femur (including, specifically, the proximal and distal portions), the pelvis, the spine, and the rib cage.
Conventional ultrasound imaging utilizes the B-mode images. B-mode images are constructed by extracting an envelope of received scanned lines of radiofrequency (“RF”) signals using the Hilbert transformation. These envelopes are then decimated (causing a drop in the resolution) and converted to grayscale (usually 256 bit) to form the final B-mode image. The conversion to grayscale results in a drop in the dynamic range of the ultrasound data.
The use of ultrasound in computer aided orthopedic surgery has gained a lot of interest in the recent decade due to its relatively low cost and radiation-free nature. More particularly, A-mode ultrasound intra-operative registration has been used for computer aided orthopedic surgery and, in limited cases, in neurosurgery. Ultrasound-MRI registration has been developed utilizing B-mode ultrasound images.
Therefore, it would be desirable to develop a method of utilizing ultrasound techniques to construct 3-D patient-specific bone and cartilage models.